In Belgium, the Management Unit of the North Sea Mathematical Models (MUMM) had mobilized remote sensing aircraft since 1991 to detect and prosecute illegal oil discharges at sea. MUMM's objective was to evaluate the effectiveness and operational character of satellite services for detecting oil spills, with regard to the detection of illegal oil spills at sea, and with respect to the added value for the present aerial surveillance program. The results of this 3-mo trial combined with 14 yr of experience in airborne remote sensing, indicated that remote sensing means used for the detection of illegal oil discharges at sea increased the chances of catching a polluter red-handed and improved the collection of evidence to strengthen the value of proof. The declining number of illegal oil discharges detected and the diminishing estimated annual oil volumes suggested a deterrent effect on the merchant marine by the physical presence of a surveillance aircraft. This is an abstract of a paper presented at the 28th Arctic and Marine Oil Spill Program Technical Seminar (Calgary, Alberta 6/7-9/2005).